The present invention relates to a grease composition for use in constant velocity joints. A very high contact pressure is developed between the parts of the constant velocity joints to be lubricated and the joint parts undergo complicated rolling motions. This often results in abnormal vibration. Accordingly, the present invention relates to a grease composition for constant velocity joints, which can effectively lubricate such constant velocity joints to effectively reduce the wear of joints and to effectively reduce the occurrence of the vibration.
Examples of lubricating greases conventionally used in such constant velocity joints include a calcium complex soap thickened grease, and a lithium soap thickened grease, e.g., a grease containing sulfur-phosphorus extreme pressure agent selected from the group consisting of fats and oils sulfide, tricresylphosphate and zinc dithiophosphate.
Recently, the number of front engine drive (FF-type) motorcars have rapidly increased for ensuring light weight and making interior space as large as possible. Constant velocity joints (CVJ) essential for these motorcars are widely used. Among the CVJs, plunging constant velocity joints, in particular, tripod type constant velocity joints (TJ) and double offset type constant velocity joints (DOJ) cause complicated rolling and sliding motions during rotation under conditions at an angle and accordingly, causes slide resistance in the axial direction, which causes vibration during tick over, rolling in starting and speeding up, and beating and/or confined noise in a car at a given speed. To solve these problems, various improvement have been made for the structure of constant velocity joints. However, it is difficult to make such improvement in the light of the space occupied by the joint, weight and cost thereof, and there is a need for a grease which has good performance for reducing vibration.